1. Field of the Invention
The present invention relates to methods of using hydrocarbon fuel vapor or hydrocarbon fuel vapor mixed with engine exhaust and/or air to form hydrogen and/or carbon monoxide. In particular, the present invention provides plasma-assisted reactions to produce hydrogen and/or carbon monoxide gases which can then be consumed in an internal combustion engine to enhance engine performance and reduce engine pollution.
2. Relevant Technology
Optimizing fuel efficiency and pollutant reduction are difficult tasks for internal combustion engines. Engine efficiency and fuel utilization increase with excess oxygen in the combustion chamber, i.e., under fuel lean conditions. At the same time, however, production of nitrogen oxides (xe2x80x9cNOxxe2x80x9d), sulfur oxides (xe2x80x9cSOxxe2x80x9d), and other pollutants also increase under fuel lean conditions. As the relative amount of oxygen decreases, pushing the combustion system toward fuel rich conditions, the pollutant production decreases, but fuel utilization and thus engine efficiency also decrease. Thus, it would be advantageous to operate the combustion system under fuel lean conditions to increase engine efficiency, if ways could be found to decrease or prevent NOx and SOx emissions.
Conventional attempts at decreasing pollutant emissions typically focus on improving the quality of the hydrocarbon fuel, or removing pollutants from the exhaust gases. Purifying fuels of sulfur- and nitrogen-containing compounds reduces the amount of sulfur and nitrogen available to form NOx and SOx pollutants. However, such purification is expensive and often impractical, and cannot affect the production of NOx from nitrogen in the combustion air. Downstream purification techniques, such as catalytic converters, are limited in the amount of pollutants they can remove due to temperature and air-to-fuel ratio constraints, and recent effort has focused on supplementing catalytic converters in exhaust gas purification. For example, U.S. Pat. No. 6,029,442 discloses a method of purifying the exhaust gas stream by introducing radicals into the exhaust gas stream. The exhaust gas stream, or a diverted portion of the exhaust gas stream, is passed through a corona discharge to form oxidizing radicals, such as hydroxyl radicals, from water in the exhaust gas. The oxidizing radicals then reportedly react with pollutant species in the exhaust gases to decrease the concentration of pollutants emitted. Similarly, U.S. Pat. No. 5,863,413 discloses a method of treating exhaust gases or precombustion gases with hydroxyl radicals to reduce pollutant emission.
These conventional pollutant reduction methods increase the cost and complexity of the combustion systems, without increasing the overall efficiency, power, or fuel utilization. Moreover, these methods primarily focus on decreasing the amount of pollutants after the pollutants have formed, and do not address the problem of initial pollutant formation.
Thus, there is a need for methods which overcome the deficiencies of the prior art.
It is an object of the present invention to provide methods of increasing fuel efficiency in internal combustion engines.
It is another object of the present invention to provide methods of reducing the output of nitrogen oxides, sulfur oxides, and other pollutants from internal combustion engines.
It is another object of the present invention to provide methods of forming synthesis gas from hydrocarbon fuel vapor mixtures.
It is another object of the present invention to provide methods of directly producing hydrogen gas from hydrocarbon fuel vapors.
In one method of the present invention, fuel vapor in an internal combustion engine is reformed to produce synthesis gas, i.e., carbon monoxide and hydrogen. Liquid hydrocarbon fuel is combusted in an internal combustion engine having a combustion chamber and a fuel tank adapted to provide liquid hydrocarbon fuel to the combustion chamber, thereby forming a hot exhaust gas stream. The exhaust gas stream, which includes carbon dioxide and water, is directed to exit the combustion chamber. A starting gas mixture, comprising a first portion of the exhaust gas stream and a stream of hydrocarbon fuel vapor, is contacted with a plasma, which promotes a reforming reaction between the fuel vapor and the exhaust gas to form a product gas mixture including carbon monoxide and hydrogen. The product gas mixture can be directed into the combustion chamber and burned to produce more power. Preferably, the plasma is produced and contained in a plasma generating device which can be preheated by contact with a second portion of the hot exhaust gas stream.
In another method of the present invention, fuel vapor in an internal combustion engine is partially oxidized to produce carbon monoxide and hydrogen. Liquid hydrocarbon fuel is combusted in an internal combustion engine having a combustion chamber and a fuel tank adapted to provide liquid hydrocarbon fuel to the combustion chamber, thereby forming a hot exhaust gas stream. The hot exhaust gas stream is directed to exit the combustion chamber. A starting gas mixture, comprising air and a stream of hydrocarbon fuel vapor, is contacted with a plasma, which promotes a partial oxidation reaction between the fuel vapor and air to form a product gas mixture including carbon monoxide and hydrogen. The product gas mixture can be directed into the combustion chamber and burned to produce more power. Preferably, the plasma is contained in a plasma generating device which can be preheated by contact with at least a portion of the hot exhaust gas stream. The hydrocarbon fuel vapor and air are preferably preheated in a heat exchanger, the heat exchanger being heated by contact with at least a portion of the hot exhaust gas stream.
In another method of the present invention, fuel vapor in an internal combustion engine is plasma-treated to directly produce hydrogen gas, along with solid carbon particles and hydrocarbon gases. Liquid hydrocarbon fuel is combusted in an internal combustion engine having a combustion chamber and a fuel tank adapted to provide liquid hydrocarbon fuel to the combustion chamber, thereby forming a hot exhaust gas stream. The hot exhaust gas stream is directed to exit the combustion chamber. A stream of hydrocarbon fuel vapor is contacted with a plasma to form a product mixture including hydrogen gas, solid carbon particles, and various hydrocarbon gases. The product mixture can be directed into the combustion chamber and burned to produce more power. The hydrocarbon fuel vapor is preferably preheated in a heat exchanger, the heat exchanger being heated by contact with at least a portion of the hot exhaust gas stream.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.